1. Field of the Invention
The present invention relates to a disc drive, and, especially, to a disc drive of a tray loading type.
2. Description of the Related Art
Recently, there has been a trend for electric power consumption of a disc drive such as a CD and a DVD to increase along with increasing speed of recording and reproduction. Along with it, it has become a problem that heat and noise in a disc drive are increasing. The electric power consumption of a spindle motor can be divided into two categories of a mechanical loss and a fluid loss. The fluid loss is caused by viscous resistance of air, which acts on a disc, and is called a windage loss. Generally, electric power consumption of a spindle motor is increased in proportion to the square of the rotational speed of a disc. However, the fluid loss is increased when the rotational speed of a disc is increased, and, when the rotational speed exceeds 6000 revolutions per minute, about the half of the electric power consumption of a spindle motor becomes a fluid loss. Thereby, an increase in actual electric power consumption is not increased in proportion to the square of the rotational speed of the disc, and the increase rapidly grows.
In a current DVD disc drive, the rotational speed of a disc becomes about 10000 revolutions per minute at 16-time speed DVD recording and reproduction. Furthermore, the rotational speed of the disc becomes about 12000 revolutions per minute at 20-time speed DVD recording and reproduction. When the rotational speed of a disc is increased as described above, the fluid loss is rapidly increased, and the electric power consumption of a spindle motor is increased. The power-supply voltage of the disc drive generally is 12V, though the voltages vary depending on specifications. When the electric power consumption of a spindle motor is increased, the voltage does not meet the specification of the power-supply voltage.
As described in Japanese Patent Application Laid-Open No. 2003-228971, it has been known that it is acceptable to reduce the thickness of an air layer on the surface of a disc in order to decrease a fluid loss with respect to the disc. Especially, fluid resistance is reduced by decreasing the thickness of the air layer on the upper surface of the disc.